Disc brake grinder



March 17, 1970 w. B. ELLEGE DISC BRAKE GRINDER 3 Sheets-Sheet l INVENTOR. VIELDON B. ELLEGE Filed July 25, 1967 ATTORNEYS March 17, 1970 w. B- ELLEGE DISC BRAKE GRINDER 5 Sheets-Sheet 2 Filed July 25. 196'? T'I G q INVENTOR- VIELDON B.ELLEGE ATTORNEYS March 17, 1970 w. B. ELLEGE DISC BRAKE GRINDER 3 Sheets-Sheet 5 INVENTOR. WEI-DON l. ELLE! Filed July 25, 1967 ATTORNEYS United States Patent 3,500,589 DISC BRAKE GRINDER Weldon B. Ellege, Lansing, Micln, assignor to FMC Corporation, San Jose, Calif., a corporation of Delaware Filed July 25, 1967. Ser. No. 655,816 Int. Cl. B24b 7/02 US. Cl. 51132 4 Claims ABSTRACT OF THE DISCLOSURE A grinding device for finishing flat surfaces on disc brake rotors has a support bar from which a stub shaft extends. A grinding disc on the stub shaft has a flat front abrasive grinding face which is rotated when brought into engagement with a rotating rotor disc. The grinding disc is positioned to rotate about an axis spaced from the axis of rotation of the brake rotor. The grinding device has a pressure member With a plastic pad which is shifted to engage the back of the grinding disc between the axis of rotation of the disc and the axis of rotation of the rotor. The disc, which rotates in the same direction as the rotor before the pressure member engages the disc, rotates in the opposite direction to the rotor after the application of pressure to the disc to quickly finish the rotor surface.

BACKGROUND OF THE INVENTION The present invention relates to a grinding device for grinding a flat surface such as the sides of a disc brake rotor.

A typical disc brake rotor, which attaches to the wheel of an automobile, has a flange with an annular face on each side. During braking of the vehicle, a brake shoe mounted in the vehicle on each side of the flange engages the annular face to stop the automobile. It is desirable, for proper braking action, that the annular faces on the brake rotors be flat and smooth. However, long or hard use of the brakes tends to roughen or groove these surfaces. To restore the brakes, the rotor surfaces should be turned on a lathe to remove the irregularities from the surfaces. After turning, the surfaces should then be ground to finish the surfaces to the desired degree of smoothness.

SUMMARY OF THE INVENTION In the present invention, a simple, effective grinding device is provided to grind the opposite annular faces on a disc brake rotor. The device can be mounted on the lathe used to turn the rotor surfaces, and can be easily operated by unskilled personnel. In brief, in the preferred form of the invention, a support bar, which is held in the tool holder of the lathe, has a stub shaft extending laterally therefrom which carries a grinding disc. The grinding disc, which is freely rotatable on the stub shaft, has a flat front abrasive grinding face. By moving the lathe carriage on which the tool holder is mounted, the grinding face on the disc is brought into engagement with the annular face on one side of the disc brake rotor which is mounted for rotation in the lathe. The axis of rotation of the grinding disc, when the grinding face of the disc engages the annular face of the rotor, is parallel to but spaced from the axis of rotation of the rotor. Initially, the grinding disc is rotated in the same angular directional sense as the rotor rotates. A pressure member, mounted in the support bar parallel to the stub shaft, can be shifted into engagement with the back of the grinding disc between the axis of rotation of the grinding disc and the axis of rotation of the brake rotor. When this is done, pressure is exerted on one side of the grinding disc which is universally pivotal to a limited extent on the stub shaft. Thus, one side of the grinding disc is urged with greater Patented Mar. 17, 1970 pressure into the brake rotor, and the grinding disc rotates in a direction opposite to the direction of rotation of the brake rotor. The rotation of the grinding disc by the rotor in a direction opposite to the direction of rotation of the rotor quickly produces the desired smooth finish on the annular rotor surface. The opposite face of the disc brake rotor is then finished in the same manner.

It is therefore one object of the present invention to provide a grinder for grinding a flat rotating surface in which a flat grinding member is driven by the member being ground. It is another object of the present invention to provide a simple, effective grinder for grinding disc brake rotors. It is yet another object of the present invention to provide a grinder for grinding a flat rotating surface in which a flat grinding member is driven by the member being ground but oppositely thereto for quick effective finishing of the surface to be ground.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view in perspective of the grinding device of the present invention mounted in a lathe to grind a disc brake rotor;

FIGURE 2 is a view in perspective showing the grinding device mounted in the tool holder of the lathe to grind one of the annular surfaces on one side of the disc brake rotor;

FIGURE 3 is a view in perspective somewhat similar to FIGURE 2 but showing the grinding device mounted to grind the annular surface on the opposite side of the disc brake rotor;

FIGURE 4 is a view partly in cross-section of the grinding device;

FIGURE 5 is a schematic diagram showing some of the forces exerted on the grinding disc by the rotating brake rotor before the pressure member is shifted into engagement with the grinding disc; and

FIGURE 6 is a schematic diagram showing the direction of rotation of the grinding disc after the pressure member is shifted into engagement therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENT The disc brake rotor 10, which, in use, is attached to the wheel of an automobile, has a flange 11 with a flat annular surface 12, 13, respectively, on each side. During braking of the automobile, the surfaces 12, 13 are engaged by brake linings mounted on the automobile on each side of the flange 11. The surfaces 12, 13, which should be smooth for optimum braking, become rough, and sometimes grooved, through use. To restore the brakes, the surfaces 12, 13 are first turned and then ground to a smooth finish.

A lathe 15, which can be used in machining the disc brake rotor 10, is shown in FIGURE 1. The lathe is described in more detail in US. Patent 2,663,975. A spindle 17 (see FIGURE 2) is journaled on axis G in the housing 18 of the lathe and can be selectively connected to a motor 19 for rotation. A carriage 20 is mounted on the side of the housing and is reversibly movable thereon in a direction parallel to the spindle by reversible rotation of handwheel 21. A cross slide 22 is mounted on the carriage and is reversibly movable thereon in a direction perpendicular to the direction of travel of carriage 20 by reversible rotation of handwheel 23.

A disc brake rotor 10 which has been removed from a wheel of an automobile is mounted on an adapter '24 on the spindle and secured thereon by nut 25. For machining the two annular surfaces 12, 13 of a disc brake rotor (which constitute work surfaces), a dual track tool holder 26 is mounted on bolt 27, which extends upwardly from the cross slide, in lieu of the tool holder (identified as 3 tool support 90) shown in US. Patent 2,663,975. The [001 holder is clamped to the cross slide by nut 28 received on the bolt 27.

As shown in FIGURES l, 2 and 3, the tool holder 26 has a base portion 29 with an upstanding post 30. A groove 31, 32 on each side of the post defines a track to receive a tool support bar. A locking plate 33 is secured to the upper end of post 30 by screws 34. The plate 33 extends over a tool support bar received in groove 31 or 32 and screws 35 will firmly hold the tool support bar in the groove.

In restoring disc brake rotors, the annular surfaces 12,

13 are initially turned simultaneously by two turning tools (not shown), secured, respectively, in grooves 31 and 32 to machine annular surfaces 12 and 13. Alternately, the surfaces 12, 13 can be turned individually. After the turning operation, the surfaces 12 and 13 are finished by the grinding tool, or device, indicated generally at 40.

.As shown best in FIGURE 4, the grinding tool 40 has a support bar 41 of hexagonal cross section with a longitudinal axis D. A stub shaft 42 is threadedly received in the support bar near the end thereof and extends laterally therefrom on an axis E perpendicular to axis D. A set screw 43 is threadedly received in the support bar 41 to bear against the end of shaft 42 for tightly locking the shaft in the bar. The stub shaft 42 terminates at its outer end in a spherical ball 44.

A disc 45 has a central opening 46 into which a hub 47'- is tightly received. Hub 47 has a socket 48 with a ball seat 49 therein. The ball end of shaft 42 is received in the socket and is held therein by ring 50. An annular abra sive sheet 51 is cemented on the front face 52 of disc 45. The disc 45, which is freely rotatable on shaft 42, is capable of limited universal movement with respect to shaft 42 by virtue of the ball and socket connection between disc 45 and shaft 42.

-A pressure member, indicated at 55, is mounted in support bar 41 on an axis F parallel to the longitudinal axis E of stub shaft 42. The pressure member has a threaded stem 56 extending through the support bar adjacent the end of the bar. A knurled knob 57 is secured to the end of the stem away from the disc 45, and a plastic button, or pad 58, made of Teflon or other suitable low friction bearing material, is secured to the other end of the stem adjacent the disc 45. A set screw 59 is threadedly received in the bar to bear against stem 56 to adjust the friction force resisting the turning of the stem. The pad 58, which is in registration with disc 45, can be shifted towards or away from the back face 60 of the disc by turning the knob 57.

After the two flange surfaces 12 and 13 have been turned with lathe turning tools, the turning tools are removed from tool holder 26 and the grinding tool 40 is mounted therein. To grind surface 12, the support bar 41 of grinding tool 40 is inserted in groove 31 with the end of the bar flush with the edge of base portion 29 and with the abrasive grinding face toward surface 12, as shown in FIGURE 2. The carriage is advanced slowly by rotation of handwheel 21 until the flat abrasive grinding face 51 of the grinding disc 45 lightly touches the surface 12 which is not rotating at this time. It will be noted that the disc, which is universally movablev on shaft 42, will move to a position perpendicular to axis E of shaft 42 on contact with the rotor flange 11. The pressure pad 58 is positioned out of contact with the back of the grinding disc and the carriage 20 is backed away slightly byJgandwheel 21. The cross slide 22 is then moved in by rotation of handwheel 23 until the right edge (as viewed in FIGURE 2). of disc 45 is in registration with the inner edge of annular surface 12. The lathe spindle is then. connected to the motor to rotate the disc brake rotor, and the carriage 20 is advanced slowly until the flat grinding face of disc 45 contacts surface 11.

When the grinding disc engages the rotor flange, which is o a ing counterclockwise as ind a d y a ow P in FIGURE 5, the disc will rotate, in axis E, counterclockwise if in a position relative to the rotor as shown in FIGURE 5. It will be noted that the rotating rotor exerts an incremental force on the grinding disc at each point of contact therewith. At each point, the force acting on the grinding disc acts along a line perpendicular to the radial rotor line which extends from the axis G of rotation of the rotor to the point. Thus, the force QA transmitted from the rotating rotor to the grinding disc at point A acts along a line LA which is perpendicular to the radial line RA. Any force line, such as line LA, which passes through the axis E of rotation of the grinding disc, will have no tendency to rotate the disc either clockwise or counterclockwise. The locus of points at which forces act along lines passing through the axis of rotation of the grinding disc is represented in FIGURE 5 by line N, which, for convenience, can be designated a null line. Forces transmitted by the rotating rotor and acting on the grinding disc to the left of the null line N (as viewed in- FIGURE 5) tend to rotate the disc counterclockwise; forces transmitted -by the rotating rotor and acting on the grinding disc to the right of the null line N (as viewed in FIGURE 5) tend to rotate the disc clockwise. The influence of the force transmitted to the disc at any given point, such as B or C, will depend on the distance DB or DC of the line of force LB or LC from the axis of rotation of the grinding disc. When the grinding disc is positioned relative to the rotor as shown in FIGURE 5, the disc will rotate in the same direction (counterclockwise) as the rotating rotor as long as the pressure pad is out of engagement with the grinding disc.

The pressure pad 58 is then shifted into engagement (on axis F) with the back face 60 of the grinding disc between the axis of rotation of the rotor and the axis E of rotation of the grinding disc, as shown in FIGURE 6. The plastic Teflon pad will not prevent the disc 45 (which is made of steel) from rotating (because the disc 45 will slide with respect to the pad) but the pad will urge the right side of the disc (as viewed in FIGURE 2) into the rotating rotor with increased force. The forces transmitted from the rotating rotor to the right side of the null line N (asviewed in FIGURE 6) increase as the pad is urged into the disc, causing the grinding disc to rotate clockwise, as shown in FIGURE 6. The rotation of the grinding'disc in a direction opposite to the rotation of the rotor -quickly smoothes flange face 12, diminishing the forces which urged the grinding disc to rotate clockwise, thus slowing down the clockwise rotation of the disc. When the disc almost stops rotating, the carriage 20 is backed off.

The grinding tool is removed from groove 31, the carriage 20 is advanced, and the tool is then inserted in groove 32, with the grinding disc toward the flange face 13 as shown in FIGURE 3. The grinding steps followed to grind surface 12 are repeated for surface 13.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention as set forth in the appended claims.

Having completed a detailed description of the invention so that those skilled in the art could practice the same, I claim:

1. Apparatus for grinding a fiat work surface rotatable about an axis of work rotation comprising (a) a support,

(b) a grinding disc mounted on a shaft on said support for rotation about an axis of disc rotation spaced from said axis of work rotation, said grinding disc having a flat front abrasive surface,

(c) means, mounting said disc for universal movement on said shaft,

((1) means to move said support toward and away from said work surface,

( a p ssure membe mo nted on sa d upport be hind the grinding disc and between said axis of disc rotation and said axis of work rotation,

(f) and means for moving said pressure member into engagement with the back of said disc to urge the front abrasive surface of the grinding disc into said work surface.

2. The apparatus of claim 1 in which the pressure member has a pad of low friction bearing material at one end to engage the back of said disc.

3. Apparatus for grinding a flat work surface rotatable about an axis of work rotation comprising:

(a) a support bar,

(b) a stub shaft secured to and extending laterally from the support bar,

(c) a grinding disc mounted on the stub shaft for limited universal movement relative thereto, said grinding disc having a fiat front abrasive surface rotatable about an axis of disc rotation,

(d) a pressure member having a stem in threaded engagement with the support bar, said pressure member terminating in a low friction bearing material pad shiftable on rotation of the stem along a line into engagement with the back of the grinding disc to 6 urge the grinding disc into said work surface, said line along which the pad is shiftable lying between said axis of work rotation and said axis of disc rotation. 4. The apparatus of claim 3 in which said line along which the pad is shiftable and the axes of rotation of the disc and Work surface are parallel.

References Cited UNITED STATES PATENTS 1,142,570 6/1915 Hodny 51120 1,934,797 11/ 1933 Galey. 2,079,076 5/ 1937 Kranich 51131 X 1,928,196 9/1933 Betrancourt. 2,663,975 12/ 1953 Barrett 51-37 2,772,521 12/1956 Voytech 51-131 X 3,374,582 3/1968 Boettcher 51-131 HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.R. 51-259 

